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NASA's Juno Navigators Enable Jupiter Cyclone Discovery Jupiter's
south pole has a new cyclone. The discovery of the massive Jovian tempest occurred
on Nov. 3, 2019, during the most recent data-gathering flyby of Jupiter by NASA's
Juno spacecraft. It was the 22nd flyby during which the
solar-powered spacecraft collected science data on the gas giant, soaring only 2,175 miles (3,500
kilometers) above
its cloud tops.
The flyby also marked a victory for the mission team, whose innovative measures
kept the solar-powered spacecraft clear of what could have been a
mission-ending eclipse.
"The
combination of creativity and analytical thinking has once again paid off big
time for NASA," said Scott Bolton, Juno principal investigator from the
Southwest Research Institute in San Antonio. "We realized that the orbit
was going to carry Juno into Jupiter's shadow, which could have grave
consequences because we're solar powered. No sunlight means no power, so there
was real risk we might freeze to death. While the team was trying to figure out
how to conserve energy and keep our core heated, the engineers came up with a completely
new way out of the problem: Jump Jupiter's shadow. It was nothing less than a
navigation stroke of genius. Lo and behold, first thing out of the gate on the
other side, we make another fundamental discovery."
When
Juno first arrived at Jupiter in July 2016, its infrared and visible-light
cameras discovered giant cyclones encircling the planet's poles - nine in the
north and six in the south. Were they, like their Earthly siblings, a transient
phenomenon, taking only weeks to develop and then ebb? Or could these cyclones,
each nearly as wide as the continental U.S., be more permanent fixtures?
With
each flyby, the data reinforced the idea that five windstorms were swirling in
a pentagonal pattern around a central storm at the south pole and that the
system seemed stable. None of the six storms showed signs of yielding to allow
other cyclones to join in.
"It
almost appeared like the polar cyclones were part of a private club that seemed
to resist new members," said Bolton.
Then,
during Juno's 22nd science pass, a new, smaller cyclone churned to
life and joined the fray.
The
Life of a Young Cyclone
"Data from Juno's Jovian
Infrared Auroral Mapper [JIRAM] instrument indicates we went from a pentagon of cyclones
surrounding one at the center to a hexagonal arrangement," said
Alessandro Mura, a Juno co-investigator at the National Institute for
Astrophysics in Rome. "This new addition is smaller in stature than its six
more established cyclonic brothers: It's about the size of Texas. Maybe JIRAM
data from future flybys will show the cyclone growing to the same size as its
neighbors."
Probing
the weather layer down to 30 to 45 miles (50 to 70 kilometers) below Jupiter's
cloud tops, JIRAM captures infrared light emerging from deep inside Jupiter. Its
data indicate wind speeds of the new cyclone average 225 mph (362 kph) - comparable
to the velocity found in its six more established polar colleagues.
The
spacecraft's JunoCam also obtained visible-light imagery of the new cyclone. The
two datasets shed light on atmospheric processes of not just Jupiter but also
fellow gas giants Saturn, Uranus and Neptune as well as those of giant exoplanets
now being discovered; they even shed light on atmospheric processes of Earth's
cyclones.
"These cyclones are new
weather phenomena that have not been seen or predicted before," said Cheng
Li, a Juno scientist from the University of California, Berkeley. "Nature
is revealing new physics regarding fluid motions and how giant planet
atmospheres work. We are beginning to grasp it through observations and
computer simulations. Future Juno flybys will help us further refine our
understanding by revealing how the cyclones evolve over time."
Shadow
Jumping
Of
course, the new cyclone would never have been discovered if Juno had frozen to
death during the eclipse when Jupiter got between the spacecraft and the Sun's heat
and light rays.
Juno has been navigating in deep space since 2011. It entered an initial 53-day orbit around Jupiter
on July 4, 2016. Originally, the mission planned to reduce the size of its
orbit a few months later to shorten the period between science flybys of the
gas giant to every 14 days. But the project
team recommended to NASA to forgo the main engine burn due to concerns
about the spacecraft's fuel delivery system.
Juno's 53-day orbit provides all the science as originally planned; it just takes
longer to do so. Juno's longer life at Jupiter is what led to the need to avoid
Jupiter's shadow.
"Ever
since the day we entered orbit around Jupiter, we made sure it remained bathed
in sunlight 24/7," said Steve Levin, Juno project scientist at NASA's Jet
Propulsion Laboratory in Pasadena, California. "Our navigators and
engineers told us a day of reckoning was coming, when we would go into Jupiter's
shadow for about 12 hours. We knew that for such an extended period without
power, our spacecraft would suffer a similar fate as the Opportunity rover, when the skies of
Mars filled with dust and blocked the Sun's rays from reaching its solar
panels."
Without
the Sun's rays providing power, Juno would be chilled below tested levels,
eventually draining its battery cells beyond recovery. So the navigation team
set devised a plan to "jump the shadow," maneuvering the spacecraft
just enough so its trajectory would miss the eclipse.
"In
deep space, you are either in sunlight or your out of sunlight; there really is
no in-between," said Levin.
The
navigators calculated that if Juno performed a rocket burn weeks in advance of
Nov. 3, while the spacecraft was as far in its orbit from Jupiter as it gets, they
could modify its trajectory enough to give the eclipse the slip. The maneuver would utilize the spacecraft's reaction control system, which wasn't
initially intended to be used for a maneuver of this size and duration.
On
Sept. 30, at 7:46 p.m. EDT (4:46 p.m. PDT), the reaction control system burn began.
It ended 10 ½ hours later. The propulsive maneuver - five times longer than any
previous use of that system - changed Juno's orbital velocity by 126 mph (203 kph)
and consumed about 160 pounds (73 kilograms) of fuel. Thirty-four days later, the
spacecraft's solar arrays continued to convert sunlight into electrons unabated
as Juno prepared to scream once again over Jupiter's cloud tops.
"Thanks to
our navigators and engineers, we still have a mission," said Bolton. "What
they did is more than just make our cyclone discovery possible; they made possible
the new insights and revelations about Jupiter that lie ahead of us."
NASA's
JPL manages the Juno mission for the principal investigator, Scott Bolton, of
the Southwest Research Institute in San Antonio. Juno is part of NASA's New
Frontiers Program, which is managed at NASA's Marshall Space Flight Center in Huntsville,
Alabama, for NASA's Science Mission Directorate in Washington. The Italian
Space Agency (ASI) contributed the Jovian Infrared Auroral Mapper. Lockheed
Martin Space in Denver built and operates the spacecraft.
More
information about Juno is available at:
https://www.nasa.gov/juno
https://www.missionjuno.swri.edu
More
information on Jupiter is at:
https://www.nasa.gov/jupiter
The public
can follow the mission on Facebook and Twitter at:
https://www.facebook.com/NASAJuno
https://www.twitter.com/NASAJuno
Take a look at Juno jumping Jupiter's shadow
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